Regulation of inducible nitric oxide synthase by dietary phytoestrogen in MCF-7 human mammary cancer cells

We examined the effects of the phytoestrogen biochanin A on the growth of the MCF-7 human breast cancer cell line. The results showed that biochanin A treatment induced dose- and time-dependent inhibition on MCF-7 cell growth at concentrations above $20 \mu$g.mL$^{-1}$. An examination of treated MCF-7 cell morphology revealed condensation of the chromosome and dehydration of the cytoplasm, suggesting apoptosis as an important factor in biochanin A-related cell growth inhibition. The results also showed that at a concentration of $40 \mu$g.mL$^{-1}$, biochanin A decreased the levels of inducible nitric oxide synthase, thus inhibiting the production of nitric oxide, a known second messenger and inducer of apoptosis, and affecting the overall cell protein pattern. No significant difference in superoxide dismutase protein levels were, however detected at concentrations of 40 or $100 \mu$g.mL$^{-1}$ of biochanin A. The data suggest that the inhibitory effects of biochanin A on human breast cancer cell growth are linked to inducible nitric oxide synthase and the associated production of nitric oxide.Régulation de la NO-synthase inductible dans des cellules cancéreuses mammaires humaines MCF-7 par des phyto-œstrogènes alimentaires. Les effets d'un phyto-œstrogène, la biochanine A, sur la croissance d'une lignée cellulaire MCF-7 humaine de cancer de sein, ont été étudiés. Les résultats montrent qu'un traitement à la biochanine A a induit une inhibition dose et temps dépendante de la croissance des cellules MCF-7 pour des concentrations supérieures à $20 \mu$g.mL$^{-1}$. L'examen morphologique de cellules MCF-7 traitées révèle une condensation chromosomale et une déshydratation du cytoplasme, suggérant que l'apoptose est une facteur important de l'inhibition de croissance due à la biochanine A. A des concentrations supérieures à $40 \mu$g.mL$^{-1}$, la biochanine A diminue les taux de monoxyde d'azote synthase inductible, inhibant ainsi la production de monoxyde d'azote, second messager induisant l'apoptose et modifiant les protéines cellulaires. Cependant, aucune différence significative n'a été observée pour les taux de protéine de la superoxyde dismutase à des concentrations de 40 ou de $100 \mu$g.mL$^{-1}$ de biochanine A. Les résultats suggèrent que l'effet inhibiteur de la biochanine A sur la croissance des cellules cancéreuses humaines du sein est lié à la monoxyde d'azote synthase inductible et à la production associée de monoxyde d'azote

Growth and cell cycle regulation by isoflavones in human breast carcinoma cells

The isoflavones daidzein and biochanin A induced a biphasic growth response in T-47D human breast cancer cells. At growth stimulatory concentrations, daidzein increased the percentage of cells entering the S phase, while at a growth inhibitory concentration, daidzein obstructed the progression of the cell cycle in the G2/M phase. Biochanin A regulated the cell cycle progression in a similar manner and showed a delay in the progression from the S phase to the G2/M phase at growth inhibitory concentrations. The levels of a cell cycle regulatory protein, P53, in response to the treatment of isoflavones, were also determined. Cells that became de-attached and floated in the medium after treatment with growth inhibitory concentrations of daidzein or biochanin A, showed higher P53 levels than cells that remained attached. These results suggest that daidzein and biochanin A influence T-47D cell proliferation and cell cycle progression, and that the underlying mechanisms might be associated with the P53 protein levels